A new study by Canadian scientists says there's a quantifiable reduction in the vehicle tailpipe emissions that contribute to global warming when people are tempted by bike-friendly routes instead of driving.
And it's a bargain basement deal. "The greenhouse gas benefit from adding low-cost new cycling infrastructure can be as important as other more costly strategies," say the scientists from Montreal's McGill University.
For a 7% increase in the length of a city's cycle path network, greenhouse gas emissions can fall by 2%, they say. If that seems like a small return on investment, it's excellent compared to the cost of making public transport more environmentally friendly.
The scientists calculate that to get the same cutback in GHG levels in a major international city like Montreal, all of its diesel buses would have to be converted to hybrid technology and all of its commuter trains would have to be electrified.
That's not a cheap option compared to boosting cycling. "A 40-foot hybrid bus costs Can$450,00 (£250,000)," the scientists say, "It's equivalent to [building] approximately 5.5 km (3.5 miles) of cycle tracks."
So, creating more cycle facilities should be a no-brainer for city bosses keen to do their bit to reduce global warming.
The new study by the Canadian-based team reveals the impact of a small growth in the city's cycle path network, from 375 miles to 402 miles. In the same period, cycling became more popular and commuters switched to biking daily. The fall in commuter driving was used to estimate the reduction in greenhouse gases.
Criticisms that their calculations are optimistic are denied by the team. "Our estimates [are] more conservative than they probably are in reality," they say. That claim is backed up by a comprehensive survey just published.
Of almost 600 cyclists stopped and questioned on National Bike to Work Day in Albuquerque, New Mexico, one in three say they would not have made their trips by bike if the existing cycle paths and lanes didn't exist. In fact, a quarter of those surveyed say they would make their journey by car if the bicycle infrastructure hadn't been built and that would, of course, increase vehicle tailpipe emissions, including greenhouse gases.
"In this light, the paths and lanes have been effective at reducing vehicle trips, helping to reduce congestion and improve air quality and public health in the region," says the leader of the survey, Dr Greg Rowengould, assistant professor in the civil engineering department at the University of New Mexico.